Various alarm devices have been proposed heretofore which sound or otherwise signal an alarm when a person touches the doorknob on the outside of a door leading into the premises to be protected. Examples of such prior proposals include: "Popular Electronics" magazine, February, 1969, pp. 92-93; U.S. Pat. No. 3,465,325 to Goldfarb et al.; and U.S. Pat. Nos. 3,508,239 and 3,623,063 to John V. Fontaine.
Touch-activated switch circuits of general application are shown in: U.S. Pat. Nos. 3,530,310 and 3,549,909 to Adelson et al.; U.S. Pat. No. 3,549,905 to Johnson; "Popular Electronics" magazine, April, 1969, pp. 56-58; and "Popular Science" magazine, February, 1973, pp. 124-125.